1. Field
This invention relates to electrolysis apparatus and to electrode structures in such apparatus.
2. State of the Art
As a result of recent shortages in hydrocarbon fuels and the recognition that the supply of such fuels will ultimately be exhausted, there has naturally been an increased interest in finding and developing alternative fuels. Hydrogen, being one of the most abundant of all elements and being relatively pollution free when burned, is considered one of the more attractive alternatives to hydrocarbon fuels, and electrolysis is considered one of the more attractive and economically feasible methods of producing hydrogen.
Prior art electrolytic cells have typically included a container of some type for holding a liquid electrolyte and a pair of electrodes immersed in the electrolyte. Application of direct current across the electrodes produces an electrochemical reaction in which the electrolyte is decomposed into one or more gaseous products. For example, with an aqueous electrolyte, oxygen and hydrogen may be produced.
Because of the inefficiencies, portability drawbacks, and unreliability of the liquid electrolyte cells, considerable interest has centered on a fairly new technology involving solid polymer electrolytes (SPE). See, for example, "Solid Electrolytes Offer Route to Hydrogen", Chemical and Engineering News, Aug. 27, 1973; "Electrolytic Hydrogen Fuel Production with Solid Polymer Electrolyte Technology" by W. A. Titterinton and A. P. Fickett, VIII IECEC Proceedings; and "A Hydrogen-Energy System", published by American Gas Association, 1973. As described in these references, SPE is typically a solid plastic sheet of perfluorinated sulfonic acid polymer which, when saturated with water, becomes an excellent ionic conductor. The ionic conductivity results from the mobility of the hydrogen ions which move through the polymer sheet by passing from one sulfonic acid group to another. An anode and cathode are positioned on either side of the sheet and pressed thereagainst to form the desired SPE cell.
Hydrogen is produced by the SPE cell by supplying water to the anode where it is electrochemically decomposed to provide oxygen, hydrogen ions, and electrons. The hydrogen ions move through the SPE sheet to the cathode while the electrons pass through the external circuit. At the cathode, the hydrogen ions and the electrons recombine electrochemically to produce hydrogen gas.
Although the prior art SPE cell described provides a reliability and efficiency not achieved with the liquid electrolyte cell, the cell requires noble metal catalysts and is subject to breakdown much more frequently than is desirable.
Improved electrolysis apparatus utilizing the SPE cell is described in U.S. Pat. No. 4,056,452 issued to one of the applicants herein, Barrie C. Campbell, on Nov. 1, 1977. In that patent, electrolysis apparatus is disclosed having a solid polymer electrolyte membrane and a pair of electrodes disposed on either side of and in contact with the membrane. At least one of the electrodes includes a corrugated portion which presents alternating ridges and grooves. The top of the ridges are maintained in contact with the membrane and the bottoms of the grooves are spaced from the membranes to enable the flow of fluid through the grooves.
3. Objectives
It is a principal objective of the present invention to provide an improved electrolysis apparatus which is more reliable and less costly than the apparatus of the prior art. A further objective is to provide electrolysis apparatus which has improved means for supplying fluid to the anode and cathode plates, as well as improved means for withdrawing fluid and electrolysis products separately from the anode and cathode plates. A still further objective is to provide electrolysis apparatus comprising a plurality of electrolytic cells in a compact and efficient series arrangement wherein corrosion due to galvanic action within and between cells is essentially eliminated. Additional objectives are to provide maximum surface area of the electrodes in contact with the solid polymer electrolyte membrane, and to provide apparatus capable of sustained, reliable operation at high pressures.